In the cylinder head of an internal combustion engine there usually are provided obliquely formed guide bores of intake and exhaust vlaves, and in the case of machining the cylinder head to make such angular bores, there have heretofore been manufactured cylinder head positioning jigs and guide bore forming machine tools especially suited for this purpose so as to have angles corresponding to the angles of guide bores in various types of internal combustion engines, because it is necessary to produce internal combustion engines in large quantities. Boring by cutting and other machining operations have been carried out for cylinder heads by using such manufactured jigs and machine tools. In automotive combustion engines, however, various types involving changes of the guide bore angle have recently been designed and manufactured because of diversification of demands, thus requiring an increased equipment cost. Particularly, in the case of conveyance pallet type jigs, there arises a problem with respect to space for storing the aforesaid jigs manufactured in large quantities because such type of jigs are relatively bulky. Besides, cylinder head positioning jigs must be machined to a high accuracy, and therefore it is very disadvantageous with respect to cost to manufacture new jigs for each new type of internal combustion engine. Under such circumstances, significant problems arise in attempting to manufacture a jig and a machine tool applicable to several types of internal combustion engines.